Trailers can be connected to tow vehicles by any of a variety of hitches, ranging from simple ball hitches and receiver hitches to heavy-duty gooseneck and fifth wheel hitches. The selection of hitch for any particular application depends on a number of factors, including the type of vehicle, the dimensions and weight of the trailer, and the anticipated load (including the weight, dimensions, and type of load). Hitches are available for virtually any motor vehicle on the market today: ball type hitches and receiver hitches are more commonly used with passenger vehicles and light trucks (automobiles, pick-up trucks, and sport-utility vehicles) for light-duty hauling. Gooseneck and fifth wheel type hitches are typically used with heavy-duty pickup trucks and tractor-trailers for hauling heavier loads.
While in motion, all vehicles and all trailers tend to bounce or sway to some degree; the extent of such bouncing or swaying motion depends on the vehicle's speed and road conditions. When a trailer is attached to a tow vehicle by a standard lock-down or solid connection hitch, the trailer cannot move independently of the vehicle. As a result, any bouncing, swaying, and vibration of the trailer is transferred directly to the vehicle through the hitch, leading at best to an uncomfortable ride for the driver and passengers. Movement of the trailer relative to the vehicle may result in the application of forces to the vehicle in one or all of the vertical direction, the horizontal direction and/or about a longitudinal axis (e.g., a torque/moment) defined by the direction of travel of the vehicle and trailer. The safety of the driver and passengers is compromised whenever the forces exerted by the relative movement of the trailer makes it more difficult to control the vehicle, for example, if the driver encounters high bumps, dips, railroad tracks, elevation changes, expansion joints, and situations that require emergency braking (which can cause jack-knifing) or other avoidance maneuvers. As the trailer bobs, bounces, and weaves, the rear end of the vehicle can sometimes be lifted off the road; the front end of the vehicle may also be lifted in turn and pushed from side to side, creating extremely dangerous conditions.
Several attempts to alleviate the problems associated with solid connection hitches have been proposed. For instance, a number of fifth wheel hitches have been designed that include a frame having one end pivotally connected to the tow vehicle and a second end supported by one or more air bags. Typically, the fifth wheel or hitch plate is supported by the frame and is disposed between the pivotally connected end and the air bag supported end. Such arrangements allows for limited relative movement (e.g., vertical movement) between a vehicle and a fifth wheel trailer connected to the fifth wheel. However, such arrangements typically permit no side-to-side movement (horizontal movement) or torsional movement between the vehicle and the fifth wheel trailer.